Prior art and the invention will be described hereinafter referring to the use of such a nozzle in a fluidized bed reactor of a generic type, thereby referring to the typical mounting position of such a nozzle in a fluidized bed of a fluidized bed reactor, i.e. with a substantially vertical orientation and an air outflow opening at the upper end section of said nozzle.
Usually fluidized bed reactors are in the form of combustors, boilers, gasifiers etc. They comprise a grid (also called a grate or a perforated plate) supporting a bed of particulate material, including a fuel material like coal, sand and ash. Air is introduced into said bed by means of nozzles. As a result of said air which is fed into and passing the bed the bed receives a fluid like state. The grid typically comprises openings to remove excessive material out of the reaction chamber.
Various types of air distribution nozzles are known in prior art. One type of those known nozzles is characterized by the following features in its functional position:                a gas inlet pipe, having        an inner surface, an outer surface, a lower end section adapted to receive air from an associated air source, and an upper end section,        an air distribution cap, having        an upper boundary, fixed to the upper end section of the gas inlet pipe,        a lower bottom, arranged at a vertical distance below said upper boundary and surrounding the gas inlet pipe,        a peripheral wall, having an inner surface and an outer surface and extending between said upper boundary and said lower bottom, thereby defining at least one space between corresponding sections of the outer surface of the gas inlet pipe and the inner surface of the wall of the air distributor cap,        first air outlet means allowing an air flow from the central gas inlet pipe into the space and        a plurality of second air outlet means allowing an air flow from said space into an ambient area,        first and second air outlet means are arranged vertically offset.        
This design is similar to a mushroom with its shaft being the gas inlet pipe and its head presenting the air distribution cap. In other words:
Air is fed vertically upward through the gas inlet pipe, fed through the first air outlet means into the mostly annular space between gas inlet pipe and air distribution cap and further in a substantially horizontal direction through said second air outlet means and insofar through said cap wall into the surrounding area, for example into the fluidized bed of a fluidized bed reactor.
The second air outlet means (openings) are designed as through holes of circular cross section. This leads to a corresponding focused and defined air stream of high velocity into the associated fluidized bed.
Although these nozzles have been used to great extent there is a continuous demand for improvements. In this context it was asserted that the fluidized bed often contains larger particles formed during combustion and/or gasification, which particles cannot be fluidized and cannot move freely in the direction of the grid outlet openings. These larger solid particles may cause damage and wear to the grid and the nozzles; they further reduce the efficiency of the fluidized bed.